Identification of yellow lake pigments in paintings by Rembrandt and Vermeer: the state of the art revisited

The identification of natural yellow organic pigments known as yellow lakes presents an analytical challenge, due to their structural complexity, poor stability, the need for invasive sampling, and the capabilities of the existing analytical methods and instrumentation. In recent years, high-performance liquid chromatography, quadrupole time-of-flight mass spectrometry (HPLC-qToF-MS) has emerged as a powerful tool for museum scientists, allowing for high resolution, molecular level analysis of organic colorants in microscopic samples. To achieve deep, rich shadows in his paintings, Rembrandt mixed and layered translucent red and yellow lakes with opaque pigments; however, the composition of the yellow lakes had not been identified until the present study. To create dark translucent greens in the backgrounds of his compositions, Vermeer also chose yellow lake pigments mixed with blue and green. These yellow lakes have been difficult to identify until now. In this study, HPLC-qToF-MS was used to identify yellow lakes in two paintings by Vermeer and one by Rembrandt, to better understand the original appearance of the paint passages where these lakes were used, and to gain further insight into these artists’ techniques. In Aristotle with a Bust of Homer, several flavonoids and an anthraquinone from a Rhamnus species were identified in a painting by Rembrandt. To the best of our knowledge, this is the first time that Rhamnus has been unequivocally identified in a 17th-century Dutch painting, despite being widely discussed in the historical literature. The analysis of samples from Vermeer’s Mistress and Maid and Study of a Young Woman detected a yellow lake based on weld, which was mixed with indigo and a copper-based green pigment. These pigment mixtures were originally dark translucent green, which have now discolored to brownish greens.